Bulk Yttria as a Host for Lanthanides in Biomedical Applications: Influence of Concentration Gradients on Structural, Mechanical, Optical, and in Vitro Imaging Behavior

The biomedical application of yttria (Y₂O₃) as a bulk material to host a series of rare earth elements (RE³⁺) has been explored in the current investigation. Dy³⁺, Gd³⁺, Tb³⁺, Yb³⁺, Eu³⁺, and Nd³⁺ were chosen for this purpose, and their corresponding concentrations in Y₂O₃ have been varied to obtain five different combinations. The results ascertain the potential of Y₂O₃ to host different RE³⁺ to retain a discrete cubic yttria (c-Y₂O₃) devoid of significant structural distortion until 1400 °C. Depending upon the size of RE³⁺, either a contracted or expanded cubic Y₂O₃ unit cell has been determined from the XRD and Raman analyses. Other than the typical vibrational modes of c-Y₂O₃, Raman spectra also unveiled characteristic emission features of RE³⁺ that were dependent on the excitation laser used to record the spectra. The characteristic absorption and emission characteristics depending on the type of RE³⁺ substitutions were determined from the optical measurements. Pore free microstructures determined from the morphological analysis are reflected in the enhanced mechanical behavior of RE³⁺ doped Y₂O₃ specimens. Dy³⁺ and Yb³⁺ substituted Y₂O₃ unveiled computed tomography (CT) imaging features. Dy³⁺, Tb³⁺, and Nd³⁺ dopant compositions delivered T₂ magnetic resonance imaging (MRI) contrast features, while the specimen comprising Gd³⁺ revealed both T₁ and T₂ MRI characteristics.